1. FIELD OF THE INVENTION
This invention relates to a monitoring system and, more particularly, to the monitoring of an electrical load to detect current fluctuations within proscribed levels.
2. DESCRIPTION OF THE PRIOR ART
It is customary to utilize conventional analog devices such as ammeters to monitor electrical underloading particularly in the plastic molding industry where the underloading of electrical zone heaters in compression and injection presses must be carefully controlled. In such systems it is common to employ one ammeter per zone when operating a compression press having a two zone heater circuit, whereas, several ammeters may be used to monitor an injection molding press having a four zone circuit. Each zone incorporates a plurality of heaters.
Unfortunately, the use of an ammeter to monitor current in a heater is not desirable because the operator is required to observe a needle on a scaled background over an extended period and this creates in the viewer a mindset which dulls operator awareness. The routine is such that operating personnel have difficulty in detecting incremental fluctuations so that over a period of time a gradual and unobservable shift may occur which puts the molding operation in jeopardy.
In plastic molding operations the failure of a zone heater is particularly critical because the ability of thermoplastic resins to plasticize and cure depend upon a carefully controlled system in which temperature variations are avoided.
The present invention avoids such occurrences by providing means for detecting wide fluctuations in temperature and rectifying heater malfunctions with dispatch so that the presses can be restored to a useful and profitable condition with a minimum of down-time.